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                    8.逃逸分析技术
            
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                    2.并行程序基础
            
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                    12.面试题一
            
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                    1.集合架构
            
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                    2.hashMap底层原理
            
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                    三种工厂模式
            
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                    实战工厂模式
            
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                    1.mysql索引基础之b树与b+树⭐⭐
            
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                    2.mysql索引及优化⭐⭐⭐⭐
            
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                    4.多版本并发控制之mvcc原理
            
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                    5.mysql事务
            
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                    6.mysql的锁机制
            
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        <a href="../.." >5.ThreadLocal.md</a>
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                                <p><strong>&#x5982;&#x679C;&#x60F3;&#x5B9E;&#x73B0;&#x6BCF;&#x4E00;&#x4E2A;&#x7EBF;&#x7A0B;&#x90FD;&#x6709;&#x81EA;&#x5DF1;&#x7684;&#x4E13;&#x5C5E;&#x672C;&#x5730;&#x53D8;&#x91CF;&#x8BE5;&#x5982;&#x4F55;&#x89E3;&#x51B3;&#x5462;&#xFF1F;</strong> JDK&#x4E2D;&#x63D0;&#x4F9B;&#x7684;<code>ThreadLocal</code>&#x7C7B;&#x6B63;&#x662F;&#x4E3A;&#x4E86;&#x89E3;&#x51B3;&#x8FD9;&#x6837;&#x7684;&#x95EE;&#x9898;&#x3002; <strong><code>ThreadLocal</code>&#x7C7B;&#x4E3B;&#x8981;&#x89E3;&#x51B3;&#x7684;&#x5C31;&#x662F;&#x8BA9;&#x6BCF;&#x4E2A;&#x7EBF;&#x7A0B;&#x7ED1;&#x5B9A;&#x81EA;&#x5DF1;&#x7684;&#x503C;&#xFF0C;&#x53EF;&#x4EE5;&#x5C06;<code>ThreadLocal</code>&#x7C7B;&#x5F62;&#x8C61;&#x7684;&#x6BD4;&#x55BB;&#x6210;&#x5B58;&#x653E;&#x6570;&#x636E;&#x7684;&#x76D2;&#x5B50;&#xFF0C;&#x76D2;&#x5B50;&#x4E2D;&#x53EF;&#x4EE5;&#x5B58;&#x50A8;&#x6BCF;&#x4E2A;&#x7EBF;&#x7A0B;&#x7684;&#x79C1;&#x6709;&#x6570;&#x636E;&#x3002;**</strong>&#x5982;&#x679C;&#x4F60;&#x521B;&#x5EFA;&#x4E86;&#x4E00;&#x4E2A;<code>ThreadLocal</code>&#x53D8;&#x91CF;&#xFF0C;&#x90A3;&#x4E48;&#x8BBF;&#x95EE;&#x8FD9;&#x4E2A;&#x53D8;&#x91CF;&#x7684;&#x6BCF;&#x4E2A;&#x7EBF;&#x7A0B;&#x90FD;&#x4F1A;&#x6709;&#x8FD9;&#x4E2A;&#x53D8;&#x91CF;&#x7684;&#x672C;&#x5730;&#x526F;&#x672C;&#xFF0C;&#x8FD9;&#x4E5F;&#x662F;<code>ThreadLocal</code>&#x53D8;&#x91CF;&#x540D;&#x7684;&#x7531;&#x6765;&#x3002;&#x4ED6;&#x4EEC;&#x53EF;&#x4EE5;&#x4F7F;&#x7528; <code>get&#xFF08;&#xFF09;</code> &#x548C; <code>set&#xFF08;&#xFF09;</code> &#x65B9;&#x6CD5;&#x6765;&#x83B7;&#x53D6;&#x9ED8;&#x8BA4;&#x503C;&#x6216;&#x5C06;&#x5176;&#x503C;&#x66F4;&#x6539;&#x4E3A;&#x5F53;&#x524D;&#x7EBF;&#x7A0B;&#x6240;&#x5B58;&#x7684;&#x526F;&#x672C;&#x7684;&#x503C;&#xFF0C;&#x4ECE;&#x800C;&#x907F;&#x514D;&#x4E86;&#x7EBF;&#x7A0B;&#x5B89;&#x5168;&#x95EE;&#x9898;&#x3002;**</p>
<h4 id="&#x539F;&#x7406;"><a name="&#x539F;&#x7406;" class="anchor-navigation-ex-anchor" href="#&#x539F;&#x7406;"><i class="fa fa-link" aria-hidden="true"></i></a><a name="&#x539F;&#x7406;" class="plugin-anchor" href="#&#x539F;&#x7406;"><i class="fa fa-link" aria-hidden="true"></i></a>&#x539F;&#x7406;</h4>
<pre><code class="lang-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Thread</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">Runnable</span> </span>{
 ......
<span class="hljs-comment">//&#x4E0E;&#x6B64;&#x7EBF;&#x7A0B;&#x6709;&#x5173;&#x7684;ThreadLocal&#x503C;&#x3002;&#x7531;ThreadLocal&#x7C7B;&#x7EF4;&#x62A4;</span>
ThreadLocal.ThreadLocalMap threadLocals = <span class="hljs-keyword">null</span>;

<span class="hljs-comment">//&#x4E0E;&#x6B64;&#x7EBF;&#x7A0B;&#x6709;&#x5173;&#x7684;InheritableThreadLocal&#x503C;&#x3002;&#x7531;InheritableThreadLocal&#x7C7B;&#x7EF4;&#x62A4;</span>
ThreadLocal.ThreadLocalMap inheritableThreadLocals = <span class="hljs-keyword">null</span>;
 ......
}
</code></pre>
<p>&#x4ECE;&#x4E0A;&#x9762;<code>Thread</code>&#x7C7B; &#x6E90;&#x4EE3;&#x7801;&#x53EF;&#x4EE5;&#x770B;&#x51FA;<code>Thread</code> &#x7C7B;&#x4E2D;&#x6709;&#x4E00;&#x4E2A; <code>threadLocals</code> &#x548C; &#x4E00;&#x4E2A; <code>inheritableThreadLocals</code> &#x53D8;&#x91CF;&#xFF0C;&#x5B83;&#x4EEC;&#x90FD;&#x662F; <code>ThreadLocalMap</code> &#x7C7B;&#x578B;&#x7684;&#x53D8;&#x91CF;,&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x628A; <code>ThreadLocalMap</code> &#x7406;&#x89E3;&#x4E3A;<code>ThreadLocal</code> &#x7C7B;&#x5B9E;&#x73B0;&#x7684;&#x5B9A;&#x5236;&#x5316;&#x7684; <code>HashMap</code>&#x3002;&#x9ED8;&#x8BA4;&#x60C5;&#x51B5;&#x4E0B;&#x8FD9;&#x4E24;&#x4E2A;&#x53D8;&#x91CF;&#x90FD;&#x662F;null&#xFF0C;&#x53EA;&#x6709;&#x5F53;&#x524D;&#x7EBF;&#x7A0B;&#x8C03;&#x7528; <code>ThreadLocal</code> &#x7C7B;&#x7684; <code>set</code>&#x6216;<code>get</code>&#x65B9;&#x6CD5;&#x65F6;&#x624D;&#x521B;&#x5EFA;&#x5B83;&#x4EEC;&#xFF0C;&#x5B9E;&#x9645;&#x4E0A;&#x8C03;&#x7528;&#x8FD9;&#x4E24;&#x4E2A;&#x65B9;&#x6CD5;&#x7684;&#x65F6;&#x5019;&#xFF0C;&#x6211;&#x4EEC;&#x8C03;&#x7528;&#x7684;&#x662F;<code>ThreadLocalMap</code>&#x7C7B;&#x5BF9;&#x5E94;&#x7684; <code>get()</code>&#x3001;<code>set()</code>&#x65B9;&#x6CD5;&#x3002;</p>
<p><code>ThreadLocal</code>&#x7C7B;&#x7684;<code>set()</code>&#x65B9;&#x6CD5;</p>
<pre><code class="lang-java">    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">set</span><span class="hljs-params">(T value)</span> </span>{
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        <span class="hljs-keyword">if</span> (map != <span class="hljs-keyword">null</span>)
            map.set(<span class="hljs-keyword">this</span>, value);
        <span class="hljs-keyword">else</span>
            createMap(t, value);
    }
    <span class="hljs-function">ThreadLocalMap <span class="hljs-title">getMap</span><span class="hljs-params">(Thread t)</span> </span>{
        <span class="hljs-keyword">return</span> t.threadLocals;
    }
</code></pre>
<p><strong>&#x6700;&#x7EC8;&#x7684;&#x53D8;&#x91CF;&#x662F;&#x653E;&#x5728;&#x4E86;&#x5F53;&#x524D;&#x7EBF;&#x7A0B;&#x7684; <code>ThreadLocalMap</code> &#x4E2D;&#xFF0C;&#x5E76;&#x4E0D;&#x662F;&#x5B58;&#x5728; <code>ThreadLocal</code> &#x4E0A;&#xFF0C;ThreadLocal &#x53EF;&#x4EE5;&#x7406;&#x89E3;&#x4E3A;&#x53EA;&#x662F;ThreadLocalMap&#x7684;&#x5C01;&#x88C5;&#xFF0C;&#x4F20;&#x9012;&#x4E86;&#x53D8;&#x91CF;&#x503C;&#x3002;</strong></p>
<p><strong>&#x6BCF;&#x4E2A;Thread&#x4E2D;&#x90FD;&#x5177;&#x5907;&#x4E00;&#x4E2A;ThreadLocalMap&#xFF0C;&#x800C;ThreadLocalMap&#x53EF;&#x4EE5;&#x5B58;&#x50A8;&#x4EE5;ThreadLocal&#x4E3A;key&#x7684;&#x952E;&#x503C;&#x5BF9;&#x3002;</strong> &#x6BD4;&#x5982;&#x6211;&#x4EEC;&#x5728;&#x540C;&#x4E00;&#x4E2A;&#x7EBF;&#x7A0B;&#x4E2D;&#x58F0;&#x660E;&#x4E86;&#x4E24;&#x4E2A; <code>ThreadLocal</code> &#x5BF9;&#x8C61;&#x7684;&#x8BDD;&#xFF0C;&#x4F1A;&#x4F7F;&#x7528; <code>Thread</code>&#x5185;&#x90E8;&#x90FD;&#x662F;&#x4F7F;&#x7528;&#x4EC5;&#x6709;&#x90A3;&#x4E2A;<code>ThreadLocalMap</code> &#x5B58;&#x653E;&#x6570;&#x636E;&#x7684;&#xFF0C;<code>ThreadLocalMap</code>&#x7684; key &#x5C31;&#x662F; <code>ThreadLocal</code>&#x5BF9;&#x8C61;&#xFF0C;value &#x5C31;&#x662F; <code>ThreadLocal</code> &#x5BF9;&#x8C61;&#x8C03;&#x7528;<code>set</code>&#x65B9;&#x6CD5;&#x8BBE;&#x7F6E;&#x7684;&#x503C;&#x3002;<code>ThreadLocal</code> &#x662F; map&#x7ED3;&#x6784;&#x662F;&#x4E3A;&#x4E86;&#x8BA9;&#x6BCF;&#x4E2A;&#x7EBF;&#x7A0B;&#x53EF;&#x4EE5;&#x5173;&#x8054;&#x591A;&#x4E2A; <code>ThreadLocal</code>&#x53D8;&#x91CF;&#x3002;&#x8FD9;&#x4E5F;&#x5C31;&#x89E3;&#x91CA;&#x4E86;ThreadLocal&#x58F0;&#x660E;&#x7684;&#x53D8;&#x91CF;&#x4E3A;&#x4EC0;&#x4E48;&#x5728;&#x6BCF;&#x4E00;&#x4E2A;&#x7EBF;&#x7A0B;&#x90FD;&#x6709;&#x81EA;&#x5DF1;&#x7684;&#x4E13;&#x5C5E;&#x672C;&#x5730;&#x53D8;&#x91CF;&#x3002;</p>
<h4 id="&#x5185;&#x5B58;&#x6CC4;&#x9732;"><a name="&#x5185;&#x5B58;&#x6CC4;&#x9732;" class="anchor-navigation-ex-anchor" href="#&#x5185;&#x5B58;&#x6CC4;&#x9732;"><i class="fa fa-link" aria-hidden="true"></i></a><a name="&#x5185;&#x5B58;&#x6CC4;&#x9732;" class="plugin-anchor" href="#&#x5185;&#x5B58;&#x6CC4;&#x9732;"><i class="fa fa-link" aria-hidden="true"></i></a>&#x5185;&#x5B58;&#x6CC4;&#x9732;</h4>
<p><code>ThreadLocalMap</code> &#x4E2D;&#x4F7F;&#x7528;&#x7684; key &#x4E3A; <code>ThreadLocal</code> &#x7684;&#x5F31;&#x5F15;&#x7528;,&#x800C; value &#x662F;&#x5F3A;&#x5F15;&#x7528;&#x3002;&#x6240;&#x4EE5;&#xFF0C;&#x5982;&#x679C; <code>ThreadLocal</code> &#x6CA1;&#x6709;&#x88AB;&#x5916;&#x90E8;&#x5F3A;&#x5F15;&#x7528;&#x7684;&#x60C5;&#x51B5;&#x4E0B;&#xFF0C;&#x5728;&#x5783;&#x573E;&#x56DE;&#x6536;&#x7684;&#x65F6;&#x5019;&#x4F1A; key &#x4F1A;&#x88AB;&#x6E05;&#x7406;&#x6389;&#xFF0C;&#x800C; value &#x4E0D;&#x4F1A;&#x88AB;&#x6E05;&#x7406;&#x6389;&#x3002;&#x8FD9;&#x6837;&#x4E00;&#x6765;&#xFF0C;<code>ThreadLocalMap</code> &#x4E2D;&#x5C31;&#x4F1A;&#x51FA;&#x73B0;key&#x4E3A;null&#x7684;Entry&#x3002;&#x5047;&#x5982;&#x6211;&#x4EEC;&#x4E0D;&#x505A;&#x4EFB;&#x4F55;&#x63AA;&#x65BD;&#x7684;&#x8BDD;&#xFF0C;value &#x6C38;&#x8FDC;&#x65E0;&#x6CD5;&#x88AB;GC &#x56DE;&#x6536;&#xFF0C;&#x8FD9;&#x4E2A;&#x65F6;&#x5019;&#x5C31;&#x53EF;&#x80FD;&#x4F1A;&#x4EA7;&#x751F;&#x5185;&#x5B58;&#x6CC4;&#x9732;&#x3002;ThreadLocalMap&#x5B9E;&#x73B0;&#x4E2D;&#x5DF2;&#x7ECF;&#x8003;&#x8651;&#x4E86;&#x8FD9;&#x79CD;&#x60C5;&#x51B5;&#xFF0C;&#x5728;&#x8C03;&#x7528; <code>set()</code>&#x3001;<code>get()</code>&#x3001;<code>remove()</code> &#x65B9;&#x6CD5;&#x7684;&#x65F6;&#x5019;&#xFF0C;&#x4F1A;&#x6E05;&#x7406;&#x6389; key &#x4E3A; null &#x7684;&#x8BB0;&#x5F55;&#x3002;&#x4F7F;&#x7528;&#x5B8C; <code>ThreadLocal</code>&#x65B9;&#x6CD5;&#x540E; &#x6700;&#x597D;&#x624B;&#x52A8;&#x8C03;&#x7528;<code>remove()</code>&#x65B9;&#x6CD5;</p>

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